Governmental mass relocations of unemployed Brazilian families from coastal foci endemic for schistosomiasis to agricultural colonies in the interior of Northeast Brazil are occurring at a rapid rate. Many of these agricultural colonies are in close association with irrigation projects which are made up of many small water ways which serve as ideal habitats for potential vector snails. The potential vector snail in this area is Biomphalaria straminea and its has recently been shown to be susceptible to Schistosoma mansoni. Therefore, B. straminea may be an important vector for the spread of schistosomiasis in these areas due to its distribution and its association with high levels of infection. The objectives of this proposed project are to: (1) investigate under laboratory conditions the susceptibility of various geographical isolates of B. straminea from the newly developed agricultural colonies; (2) examine the infectivity of cercariae produced by B. straminea under laboratory conditions; (3) examine field collected B. straminea in and near newly developed agricultural colonies for naturally-acquired infections of S. mansoni; (4) verify the identity of B. straminea and/or other vector snails collected in or near the agricultural developmental colonies; and, (5) delineate geographical areas of occurrence of B. straminea and/or other snails which possess the ability to serve as a vector for S. mansoni. The proposed research dealing with snail biology and intermediate host-parasite relationships is vital to the formulation of control strategies. The economic benefit brought by irrigation practices can be hindered by the great loss due to the disease unless effective control measures are taken.